In recent years, the requirement for reduction in thickness and size of a semiconductor chip have become intensified with the higher integration of electronic equipment. When an extremely thin semiconductor chip is intended to be obtained and mounted on a device, there is employed a method of subjecting the surface opposite to a circuit pattern-forming surface having a bump and the like of a semiconductor wafer to polishing and grinding work before the semiconductor wafer is divided into chips and then subjecting the resulting semiconductor wafer to a dicing step of cutting it individual chips.
In order to prevent the circuit pattern surface of a semiconductor wafer from being damaged or being polluted with polishing waste, polishing water, and the like during such a step, it is necessary to protect the circuit pattern-forming surface of a semiconductor wafer.
Further, a semiconductor wafer has a problem of being easily damaged even with slight external force since it is thin and brittle by itself as well as the surface of a circuit pattern has unevenness.
For the purpose of protecting the circuit pattern surface and preventing the breakage of a semiconductor wafer during the processing of such a semiconductor wafer, there is known a method of laminating a back grinding sheet to the circuit pattern surface of a semiconductor wafer during polishing and grinding work.
Further, the followability to the unevenness of a circuit pattern-forming surface having a bump or the like of a semiconductor wafer is also required for such a pressure sensitive adhesive sheet.
When a pressure sensitive adhesive sheet having an insufficient followability to unevenness is used, the adhesion between the pressure sensitive adhesive layer of the pressure sensitive adhesive sheet and the surface of the semiconductor wafer will be insufficient. As a result, during the polishing work, there may be peeling of a pressure sensitive adhesive sheet, infiltration of polishing waste and polishing water into a pattern-forming surface, working failure, occurrence of dimples, occurrence of chip flying and the like, and even damage of a semiconductor wafer.
Various pressure sensitive adhesive sheets are proposed aiming at the development of a pressure sensitive adhesive sheet that can solve the above problems.
For example, for the purpose of providing a pressure sensitive adhesive sheet for holding and protecting a semiconductor wafer which can follow the unevenness of a wafer surface and can prevent wafer contamination and a wafer crack, Patent Document 1 discloses a pressure sensitive adhesive sheet in which there is provided, on one side of a base material layer, an intermediate layer having a predetermined modulus of elasticity and gel fraction and containing an acrylic polymer and a radiation curable oligomer, and a radiation curable pressure sensitive adhesive layer is formed on a surface of the intermediate layer.